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Tue, 04 Aug 2026 02:01:19 -0700 (PDT) From: Qihang To: netdev@vger.kernel.org Cc: willemdebruijn.kernel@gmail.com, willemb@google.com, daniel.zahka@gmail.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, stable@vger.kernel.org, Qihang Tang Subject: [PATCH net v6 1/3] net: remove CAP_SYS_RAWIO zero-padding in dev_validate_header Date: Tue, 4 Aug 2026 17:00:14 +0800 Message-ID: <20260804090016.33353-2-q.h.hack.winter@gmail.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20260804090016.33353-1-q.h.hack.winter@gmail.com> References: <20260730082925.93759-1-q.h.hack.winter@gmail.com> <20260804090016.33353-1-q.h.hack.winter@gmail.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Qihang Tang dev_validate_header() reads dev->hard_header_len directly when zero-padding short link layer headers for CAP_SYS_RAWIO holders: if (capable(CAP_SYS_RAWIO)) { memset(ll_header + len, 0, dev->hard_header_len - len); return true; } Packet send paths call dev_validate_header() on skbs whose headroom was allocated from an earlier hard_header_len read. If the device is reconfigured so that dev->hard_header_len increases before validation, the memset writes past the reserved buffer, an out-of-bounds write. This out-of-bounds write is masked in some SOCK_RAW paths today because the same concurrent increase can first make skb_push() exceed the reserved headroom and trigger skb_under_panic(). Remove the zero-padding branch before making those hard_header_len reads consistent, so the snapshot fixes do not turn a loud panic into a silent overwrite. This path is only reached for variable length L2 protocols, where len < hard_header_len but len >= min_header_len. No remaining in-tree variable length L2 protocol implements header_ops->validate, and the CAP_SYS_RAWIO bypass that zero-pads and accepts short headers has no real value beyond allowing testing of intentionally malformed input. Drop the CAP_SYS_RAWIO branch. The remaining reads of dev->hard_header_len in dev_validate_header() are comparisons only and have no memory safety impact. Suggested-by: Willem de Bruijn Fixes: 2793a23aacbd ("net: validate variable length ll headers") Cc: stable@vger.kernel.org Signed-off-by: Qihang Tang --- include/linux/netdevice.h | 5 ----- 1 file changed, 5 deletions(-) diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index 9981d637f8b5..9a770eb823ce 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -3531,11 +3531,6 @@ static inline bool dev_validate_header(const struct net_device *dev, if (len < dev->min_header_len) return false; - if (capable(CAP_SYS_RAWIO)) { - memset(ll_header + len, 0, dev->hard_header_len - len); - return true; - } - if (dev->header_ops && dev->header_ops->validate) return dev->header_ops->validate(ll_header, len); -- 2.50.1 (Apple Git-155)